1. Field of the Invention
Apparatuses consistent with the present invention relate to a collimating light guide plate and a diffusing unit. A display apparatus employing the collimating light guide plate and the diffusing unit shows improved optical performances such as light transmittance, viewing angle, and resolution.
2. Description of the Related Art
As portable devices, such as mobile phones, personal digital assistants (PDAs), portable multimedia players (PMPs), digital multimedia broadcasting (DMB) systems, and notebook computers, have widely prevailed in recent years, there are demands for display apparatuses having low power consumption and high outdoor visibility. Such portable devices or display apparatuses display an image using a liquid crystal panel. In this case, however, a viewing angle is narrow because of a difference in an optical path between light propagating perpendicular to a screen and light obliquely propagating to the screen. To solve the problem, attempts have been made to increase a viewing angle using a compensating film. However, there still remain gray scale inversion and color shifts, especially in the oblique viewing angle.
For example, an illumination system in which light outcoupled or extracted from a light guide plate is collimated by a prism sheet is known to one skilled in the art as a possible solution. However, there are structural limitations in collimating light using the prism sheet and resolution is sacrificed. Also, other attempts have been made to increase a viewing angle using a diffusing plate. That is, the diffusing plate is disposed above an upper polarizing plate of a liquid crystal panel, and an air layer is formed between the diffusing plate and the upper polarizing plate. When light passes through the diffusing plate and the upper polarizing plate, the air layer acts as an interface, thereby reducing transmittance. When used outdoors, external light is reflected by the diffusing plate and the air layer, thereby reducing visibility as well.